1. Field of the Invention
This invention relates to devices for separating particles of different sizes in a supply of particulate material and more particularly, to a vibratory particle separating apparatus for separating a supply of particulate material such as wood chips, shredded tire particles and the like, into two streams according to particle size. In a preferred embodiment, the apparatus is characterized by a particle separating screen including multiple steps shaped perpendicular to the path of material flow and mounted in sloped configuration in a mount frame. The mount frame is suspended in a support frame by resilient rubber or plastic float mounts and vibrated by a vibratory motor mounted on the mount frame. As the supply of material is loaded on the top inclined end of the vibrating screen, the material cascades down the steps of the screen and particles smaller than a selected size fall through one of multiple, adjacent openings provided in each step and are collected or discharged for further processing in a stream below the screen, whereas particles too large to fall through the opening are collected or discharged in a separate stream at the foot of the screen. In one embodiment the vibratory motion of the screen may be varied to optimize particle separation according to the characteristics of the material, by adjusting the angle of the float mounts with respect to the support frame. In another embodiment the openings in the upper step or steps on the top inclined end of the particle separating screen are omitted, or "blinded", such that elongated particles such as sticks being loaded on the screen must lie flat and slide down to the foot of the screen, instead of "diving" through one of the openings and mixing with the smaller particles being separated from the material.
Many devices are known for separating particles according to size in a stream of particulate material containing wood waste, shredded tires and the like. For example, in separation of particles in a wood waste stream, these devices are used to separate the "fines", or particles smaller than a desired size, from the "overs", or particles larger than the desired size. The "fines" are typically removed from the stream in order to reduce wear on downstream equipment which processes or sizes the larger particles, as well as to facilitate alternative processing of the material, such as drying, grit removal or by-pass of redundant sizing.
Most particle separating devices utilize a screen having an arrangement of openings, through which the "fines" may pass but the "overs" may not. After falling through the openings, the "fines" are collected or discharged for further processing in one stream, whereas the "overs" are collected or discharged from the end of the screen in a separate stream. In some instances, some of the openings have a tendency to "blind" or become plugged with particles having a size between that of the "fines" and that of the "overs". The new and improved design of this invention prevents "blinding" of the openings by the shape and orientation of the openings in the surface of the particle separating screen, such that particles having a tendency to plug the openings are either vibrated out of the openings or pushed out of the openings by the oncoming stream of material and continue sliding down to the foot of the screen.
2. Description of the Prior Art
Several devices are known in the art for separating particles in a mixture of particulate material according to particle size, weight or other characteristics. U.S. Pat. No. 4,624,370, dated Nov. 25, 1986, to Gary A. Danner, describes a "Vibratory Separation Apparatus" having upper and lower conveying surfaces separated by an opening. A mixture of particulate material is conveyed by a vibrating action beyond the upper conveying surface and through the opening. A stream of air is directed from below the upper conveying surface against the falling particles and propels particles having a predetermined density or dimension onto the lower conveying surface. U.S. Pat. No. 4,802,591, dated Feb. 7, 1989, to William E. Lower, et al, discloses a "Louvered Chip Screener" for separating chip-shaped particles according to thickness. The screener is characterized by a sloping deck having a series of spaced, flexible slats which extend parallel to the direction of chip flow. The deck is subjected to a horizontal gyratory motion such that particles smaller than a selected size fall between the slats and are collected or discharged in one stream, whereas larger particles slide down the slats and are collected or discharged at the foot of the deck. A "Vibratory Separation Apparatus" is detailed in U.S. Pat. No. 4,844,235, dated Jul. 4, 1989, to Raymond W. Sherman, in which apparatus a resilient liner is provided on the particle supporting surfaces of a vibratory conveyor system. The liner provides a surface which prevents the particles from adhering to each other and to the conveying surface and is particularly effective when used in particle separating systems. U.S. Pat. No. 5,108,589, dated Apr. 28, 1992, to Raymond W. Sherman, discloses a "Material Separating Apparatus" for separating particles of different sizes. The apparatus includes a trough having a material input end and a material discharge end, and a screen having multiple, longitudinally-spaced finger screen sections extends over the trough. As the trough is vibrated, particles smaller than a preselected size pass through the fingers, whereas larger particles move from the input end to the discharge end of the trough. A "Vibrating Conveyor Screening Method and Apparatus" for screening fine particles from a stream of particulate material, is detailed in U.S. Pat. No. 5,368,167, dated Nov. 29, 1994, to Glen E. Howes. The apparatus is characterized by first and second sets of transversely-spaced, longitudinally-extending members disposed parallel to each other. At least one of the sets is mounted to vibrate along a longitudinal axis to feed material therealong. Multiple, spaced, transversely-extending third members are located between the first and second members defining multiple screen openings between the first, second and third members. As the particulate material is passed over the apparatus, the fine particles fall through the screen openings, whereas larger particles are discharged from the end of the apparatus. A "Screen Assembly For Vibrating Screening Machine" is disclosed in U.S. Pat. No. 5,417,858, dated May 23, 1995, to William W. Derrick, et al. The screen assembly is characterized by a plate having spaced apertures and channels formed in the sides for attachment to a vibratory screening machine. Spaced frame members are provided on opposite sides of the plate and an undulating screen is mounted between the frame members above the plate. The screen includes substantially parallel ridges with downwardly-sloping sides and troughs formed between the sides for conducting the material.
An object of this invention is to provide a vibratory particle separating apparatus for separating particulate material according to particle size.
Another object of this invention is to provide a vibratory particle separating apparatus characterized by a sloped particle separating screen which vibrates responsive to operation of a vibratory motor and receives a supply of particulate material, wherein the material cascades down the vibrating screen and particles smaller than a selected size fall through openings provided in the screen and are collected or discharged below the screen and particles larger than the selected size are collected or discharged for further processing at the foot of the screen.
Still another object of this invention is to provide a vibratory particle separating apparatus for receiving and separating a supply of particulate material into two streams according to particle size, which apparatus is characterized by a vibrating particle separating screen mounted in a frame in sloped configuration and shaped in a series of steps from the top inclined end of the screen to the foot of the screen, wherein particles of a selected size fall through one of multiple openings in the steps and are collected or discharged in one stream and particles larger than the selected size cascade to the bottom end or foot of the screen and are collected or discharged in a separate stream.
Yet another object of this invention is to provide a vibratory particle separating apparatus characterized by a sloped particle separating screen including multiple steps formed therein and multiple openings included in the steps wherein particles having a tendency to plug the openings are either vibrated out of the openings or pushed out of the openings by the oncoming stream of material.